The present invention relates to a connecting rod for a reciprocating piston of an internal combustion engine, and more particularly to the crankpin bearing thereof.
In the past, the crankpin bearing of a connecting rod has typically been a two-piece construction to permit assembly of the connecting rod onto the crankpin of a crankshaft of an internal combustion engine. The two-piece construction typically includes an integral arcuate shaped portion at one end of the rigid beam or body of the connecting rod, and a corresponding arcuate shaped cap disposed in mating relationship therewith. When joined together the cap and crankpin bearing portion define the crankpin bearing and a crankpin bearing hole for receiving a crankpin of a crankshaft.
In order to properly align the cap member with respect to the integral arcuate shaped bearing portion, it is known to form a pair of shoulders or steps in the joint formed by the cap member at diametrically opposite sides of the crankpin bearing hole. The location and dimensions of these steps or shoulders were such that when the cap member was assembled on the integral arcuate shaped crankpin bearing portion of the beam the crankpin bearing became prestressed radially outwardly across its diameter. Thus, when the crankpin bearing became hot during operation, and in particular when its temperature approached its seizing temperature, the crankpin bearing would expand radially outwardly at the joint location and at the same time would expand radially inwardly at locations diametrically opposite from the joint. Essentially, the crankpin bearing would change from a circular configuration to an oval configuration. This change results in a loss of oil film between the crankpin and crankpin bearing which in turn results in scoring of the crankpin and eventually seizing of the crankpin and crankpin bearing.
Another problem with the above arrangement is that it was difficult to maintain the tolerances required in the step or shoulder formed in the joint between the cap member and arcuate bearing portion. As a result, the loss of tolerances resulted in the cap member being essentially permanently mounted on the arcuate bearing portion so that the connecting rod could not be readily disassembled for repair and maintenance.